Contemporary cellular systems, such as 3rd Generation Partnership Project (3GPP) Evolved UMTS Terrestrial Radio Access (E-UTRA) Long Term Evolution release 8 (LTE Rel-8) systems, rely on link adaptation to the existing radio environment in order to maximize the spectral efficiency. Such link adaption may relate, e.g., to Modulation and Coding Scheme (MCS), as well as different Multiple-Input and Multiple-Output (MIMO) transmission modes. The related measures from which adaptation is performed can generally be referred to as Channel State Information (CSI), and could typically include Channel Quality Indicator (CQI), transmission Rank Indicator (RI) and Precoder Matrix Index (PMI). To enable for the link adaptation, the User Equipment (UE) feeds back these measures in the uplink (UL) to the eNodeB. The Uplink Control Information (UCI) may also include acknowledgement/negative acknowledgement (ACK/NACK) in response to downlink (DL) transmissions. Thus, the UCI can include any one of, or any combination of an Ack, a Nack, a periodic CQI report, an aperiodic CQI report, a periodic RI report, a periodic PMI report, an aperiodic CQI report, an aperiodic RI report, an aperiodic PMI report, and a Scheduling Request (SR).
In LTE Rel-8, UCI is either transmitted on the Physical Uplink Control Channel (PUCCH) or on the Physical Uplink Shared Channel (PUSCH). Simultaneous transmission of PUCCH and PUSCH never occurs in the LTE Rel-8 system. Two kinds of CSI reporting methods are supported in the system; periodic CSI reporting and aperiodic CSI reporting. Periodic CSI reports are transmitted on the PUCCH and the related parameters, such as, e.g., periodicity, and transmission resources are configured by higher layers. Aperiodic CSI reports are transmitted in the PUSCH and are triggered by a CQI request bit in an UL grant in the Physical Downlink Control Channel (PDCCH) that schedules the PUSCH.
Aperiodic CSI can also be multiplexed with normal data in the PUSCH. In LTE Rel-8, in case UCI transmission in the PUCCH would occur simultaneously as a PUSCH transmission, the UCI in the PUCCH is transmitted in the PUSCH instead, and the PUCCH is not transmitted. If an aperiodic CQI report would be scheduled in the same subframe as a periodic CQI report, the periodic CQI report is not transmitted.
In LTE Rel-8, there is no carrier aggregation implemented and hence there exists no problem of determining an UL CC for transmitting UCI, and of course no solution for this has been presented.
Hence, in a radio communication system employing carrier aggregation, in case more than one PUSCH is to be transmitted in a subframe, there exists a problem in the system being related to how to determine the PUSCH on which UCI should be transmitted, such that enhanced system performance and operation are achieved.